This invention relates to a process and apparatus for the separation of a hydrocarbon stream. The applicants claim the benefits under Title 35, United States Code, Section 119(e) of prior U.S. Provisional Application No. 61/876,409 which was filed on Sep. 11, 2013, No. 61/878,977 which was filed on Sep. 17, 2013, and No. 61,879,237 which was filed on Sep. 18, 2013. Assignees S.M.E. Products LP and Ortloff Engineers, Ltd. were parties to a joint research agreement that was in effect before the invention of this application was made.
Ethylene, ethane, propylene, propane, and/or heavier hydrocarbons can be recovered from a variety of gases, such as natural gas, refinery gas, and synthetic gas streams obtained from other hydrocarbon materials such as coal, crude oil, naphtha, oil shale, tar sands, and lignite. Natural gas usually has a major proportion of methane and ethane, i.e., methane and ethane together comprise at least 50 mole percent of the gas. The gas also contains relatively lesser amounts of heavier hydrocarbons such as propane, butanes, pentanes, and the like, as well as hydrogen, nitrogen, carbon dioxide, and/or other gases. The recovered ethylene, ethane, propylene, propane, and/or heavier hydrocarbons are generally recovered as a mixed product by a gas processing plant, whereupon the mixed hydrocarbon product is then sent elsewhere for further processing and/or use as feedstock for chemical conversion and/or fuel production processes.
The present invention is generally concerned with the separation of such mixed hydrocarbon streams into a fraction containing the more volatile hydrocarbon components and a fraction containing the less volatile hydrocarbon components. Such separation is often advantageous because one or both of the products is more valuable when separated from the other product. For example, separating (deethanizing) the ethane from the natural gas liquids (NGL) produced in a gas processing plant would allow the ethane to be used as a premium feedstock for an ethylene cracking process, making it more valuable than it is as a part of the NGL stream. This separate ethane product could also be more valuable based on its gaseous fuel value than it is as part of the NGL stream when there is an over-supply of ethane in the market.
The present invention is a novel means of fractionating hydrocarbon streams that combines what heretofore have been individual equipment items into a common housing, thereby reducing both the plot space requirements and the capital cost of the addition. Surprisingly, applicants have found that the more compact arrangement also significantly reduces the power consumption required to achieve a given recovery level, thereby increasing the process efficiency and reducing the operating cost of the facility. In addition, the more compact arrangement also eliminates much of the piping used to interconnect the individual equipment items in traditional plant designs, further reducing capital cost and also eliminating the associated flanged piping connections. Since piping flanges are a potential lead source for hydrocarbons (which are volatile organic compounds, VOCs, that contribute to greenhouse gases and may also be precursors to atmospheric ozone formation), eliminating these flanges reduces the potential for atmospheric emissions that may damage the environment.
In the following explanation of the above figures, tables are provided summarizing flow rates calculated for representative process conditions. In the tables appearing herein, the values for flow rates (in moles per hour) have been rounded to the nearest whole number for convenience. The total stream rates shown in the tables include all non-hydrocarbon components and hence are generally larger than the sum of the stream flow rates for the hydrocarbon components. Temperatures indicated are approximate values rounded to the nearest degree. It should also be noted that the process design calculations performed for the purpose of comparing the processes depicted in the figures are based on the assumption of no heat leak from (or to) the surroundings to (or from) the process. The quality of commercially available insulating materials makes this a very reasonable assumption and one that is typically made by those skilled in the art.
For convenience, process parameters are reported in both the traditional British units and in the units of the Systėme International d′Unités (SI). The molar flow rates given in the tables may be interpreted as either pound moles per hour or kilogram moles per hour. The energy consumptions reported as horsepower (HP) and/or thousand British Thermal Units per hour (MBTU/Hr) correspond to the stated molar flow rates in pound moles per hour. The energy consumptions reported as kilowatts (kW) correspond to the stated molar flow rates in kilogram moles per hour.